Many motor vehicle thefts occur when vehicles are left running and unattended. Although vehicles should be shut off and locked when unattended, this is not always possible, particularly for emergency vehicles and vehicles used in extremely cold climates.
Ambulances are frequently left unattended at emergency call locations while ambulance personnel care for the injured. Since many drugs and blood supplies need to be refrigerated at constant temperatures, ambulance refrigerators are run continuously. Ambulance engines are, therefore, often left running during emergency calls to supply power to the refrigerators.
Vehicles used in very cold climates frequently require continuous heating to prevent damaging engine freeze-ups when outdoor temperatures are below 0.degree. F. Further, very cold engines are difficult to start and, when started, are susceptible to engine damage. In order to avoid this problem, vehicles in some northern states are commonly indoor-garaged or equipped with electric engine block heaters. Where neither a garage nor an electrical outlet is available, residents of these areas are forced to leave their vehicles running and risk theft.
Diesel engine vehicles are particularly susceptible to cold weather problems. The fuel oil used by these vehicles thickens at temperatures below 20.degree. F. This makes it difficult to achieve sufficiently high compression to start diesel vehicles in cold weather unless they are equipped with engine block and fuel line heaters. For this reason and because diesel vehicles are very fuel efficient at idle, many diesel vehicles are left running almost constantly in winter. As a result, trucks with valuable cargo often risk losses due to theft in winter.
A need therefore exists for an anti-theft system which permits vehicle engine operation while preventing theft.